The invention relates to a method of producing a specimen for microscopic investigation having a surface contrast, especially a color contrast, which is characteristic of the component parts of the specimen material.
In biological investigations it is well known to produce a color contrast in thin sections by staining the section with a suitable dye. This method fails, however, if the contrast is to be produced on a non-biological specimen. There are, of course, several methods known by which a contrast may be generated on the surface of a non-biological specimen, however, all these methods have serious disadvantages. There are, for example, the methods of wet etching and of anodic etching for generating colored layers on the specimen. However, these methods are limited to a few particular applications. By the so-called annealing etching method thin colored oxide layers are produced on the object surface by heating the object in a special oven. But only few objects are suitable for this kind of operation.
Further, a method of producing thin, highly refracting and light-transmissive layers on the object is known, which layers amplify considerably the natural object contrast. The layer is produced by evaporation in a high vacuum. This method, however, is only applicable in scientific research and not in routine investigations, on account of the great expenditures both of apparatuses and time.
In the so-called cathodic etching the object is bombarded in a high vacuum by high-energy positive ions with the object being connected to the cathode. The structure of the object become visible mainly by different erosion of the component parts of the object. Subsequent oxydization by positive air or oxygen ions will highly amplify the contrast. However, the exact relation between the grey shades or the color and the chemical material is greatly lost by the ion-etching.
It is, therefore, an object of the present invention to provide a simple, effective method of producing contrast, especially color contrast, on the specimen to be examined. it is a further object to provide a method which consumes only little time. And it is a further object to provide a method which may be carried out under microscopic examination so that the user may establish the process and object conditions most favorable for the specific task.